The present disclosure relates generally to semiconductor device manufacturing techniques and, more particularly, to forming nickel-platinum (NiPt) alloy self-aligned silicide contacts.
In the manufacture of semiconductor devices, salicide (or self-aligned silicide) materials are formed upon gate conductors and diffusion regions to reduce the line resistance of a CMOS device, thereby improving the speed characteristics thereof. In salicide technology, a refractory metal or a near noble metal, such as titanium for example, is deposited on a silicon substrate. The deposited metal is then annealed, thereby forming a silicide layer only on the exposed areas of the substrate. The areas of unreacted metal left on the dielectric may then be selectively etched away without a masking step. Thus, the process is “self-aligning.”
As circuit devices have continued to shrink in size, however, it has been found that titanium silicide (TiSi2) becomes an unsatisfactory silicide material since the sheet resistance thereof begins to sharply increase when the linewidth of the device decreases below 0.20 microns (μm). More recently, cobalt disilicide (CoSi2) has been used as a replacement for titanium in salicide structures since it does not suffer from a linewidth dependent sheet resistance problem. On the other hand, the use of cobalt silicide structures is not without its own drawbacks. For example, unlike titanium, a cobalt layer requires a cap layer such as titanium nitride (TiN) due to the sensitivity of cobalt to contaminants during the annealing process.
Attention has also recently turned to nickel (Ni) as a silicide metal. Among silicide constituents, nickel silicide is considered important to the development of manufacturing processes in 65 nanometer (nm) MOSFET technology and beyond because of characteristics such as low electrical resistivity, low silicon consumption, good resistance behavior in narrow lines, and low processing temperature.
Typically, forming nickel silicide contacts includes forming a nickel metal layer on a semiconductor wafer. A first rapid thermal anneal (RTA) process is then performed to react nickel with silicon to produce nickel-rich silicide. Typically Ni2Si is the first metal-rich phase that nucleates. Thereafter, a selective etching process is performed to remove the portions of the nickel metal layer that are not reacted (i.e., those portions formed on insulating layer). A second rapid thermal anneal process is then performed to complete the fabrication of the nickel silicide, which forms the low resistance NiSi phase.
However, because nickel monosilicide (NiSi) (also referred to generally as “nickel silicide”) has low thermal stability, some nickel material may penetrate through the interface between metal and silicon down to the gate electrode to cause a spiking effect. It is also possible for nickel material to laterally diffuse to the channel region, to causing a nickel “piping” effect. To improve the thermal stability of nickel silicide, several approaches have been proposed, including the use of nickel alloys, and in particular nickel-platinum (NiPt) alloys. Platinum is a noble metal element with stable chemistry properties, and is helpful to improve the thermal stability of nickel silicide. On the other hand, platinum is also a difficult metal to etch, which may results in platinum residue being present following the removal of the unreacted metal layer.